f you're not in the mood to try out a squat toilet, 99.9% of the time there's at least one stall with a Western-style sitting toilet. Just wait until one is available, and indicate to others in line that they are welcome to use the stall with the squat toilet. You may notice that the stall doors go all the way down to the floor. I guess that if people are squatting, they don't want people peeking under just to check if the stall is empty.
The only time that a squat toilet was my only option was in a more rural town than Penang. That experience had me going home and Googling "How to use a squat toilet." Believe me, for a lady, it's not as intuitive as it sounds.
Some people accustomed to squatting have the opposite culture shock problem when faced with a sitting toilet. Upon occasion, you'll notice footprints on the sitting toilet's seat. I guess that's the reason some places post this sign.